U.S. Pat. No. 4,546,060 issued Oct. 8, 1985 in the names of E. T. Miskinis and T. A. Jadwin, discloses a method of toning an electrostatic image using a rapidly rotating magnetic core. The rotating core is located inside a non-magnetic sleeve and causes a developer which includes hard magnetic carrier particles to move around the sleeve and through toning relation with the electrostatic image. Movement of the developer is caused by a rotating, rolling or tumbling action of the hard magnetic carrier particles when they are subjected to rapidly changing magnetic fields from the magnetic core. This tumbling action causes the developer to move in a direction around the sleeve opposite that of the rotating core.
The non-magnetic sleeve could also be rotated. Although it is known to rotate it in either direction, it commonly has been rotated in a direction opposite to that of the core so that it assists somewhat in moving the developer. This technology provides a soft development brush and extremely high quality development.
U.S. Pat. No. 4,671,207 issued to T. K. Hilbert Jun. 9, 1987 shows a magnetic brush in which developer is transported from a sump area to an applicator by a fluted roller. Developer is attracted to the fluted roller by a magnet inside the roller. The applicator utilizes the Miskinis and Jadwin invention, having a rotatable magnetic core within an also rotatable non-magnetic sleeve. A developer valve is positioned between the fluted roller transport and the applicator to permit turning the toning station off without moving the toning station away from an electrostatic image carrying image member. This valve or gating structure enables the toning station to not tone some electrostatic images passing it without the need for moving the entire station away from its development position. This feature is particularly usable in color electrophotographic apparatus in which different colored toners are applied to different electrostatic images.
The Hilbert patent shows a skive or a wiper positioned downstream from the development position for wiping developer off the non-magnetic sleeve to permit it to fall back into the sump for remixing. Both the skive and the non-magnetic roller in actual use are relatively smooth surfaces. The roller is smooth to prevent damage at the contact point with the skive. The skive is smooth to not resist the flow of developer as it falls under force of gravity to the sump.
U.S. Pat. No. 4,690,096 granted Sep. 1, 1987 to Hacknauer et al shows a toning station similar to that in the Hilbert patent in which the gating structure has been changed to a movable shell around and spaced from the fluted roller which shell has several openings for developer. Movement of the shell can turn the toning station to an "off" or non-toning condition. This patent also shows a wiper downstream from the development position for cleaning developer off the non-magnetic sleeve so that it can fall like gravity through the sump. For other related structure, see U.S. Pat. Nos. 4,748,471, Adkins, issued May 31, 1988 and 4,956,675, Joseph, issued Sep. 11, 1990.
U.S. Pat. No. 4,699,495 granted to Hilbert, Oct. 13, 1987, shows a structure similar to the above including a gate for preventing developer from entering the applicator housing and a movable skive or wiper which can move into and out of position against the non-magnetic sleeve. The skive is moved out of engagement with the sleeve when the gate mechanism is closed to increase the life of the skive.
U.S. Pat. No. 4,633,807, granted to Jacobs, Jan. 6, 1987, also shows a wiper or skive that is somewhat movable. It is repeatedly engaged by a mixer blade to dislodge any developer that may have a tendency to accumulate on the skive.
In U.S. Pat. No. 4,634,286 to Pike, granted Jan. 6, 1987, the downstream skive is formed as part of a housing structure which also defines an opening from the developer transport means to the applicator.
U.S. Pat. No. 4,797,704 granted to Hill et al on Jan. 10, 1989, shows a development station in which a rotating magnetic core is positioned inside an irregularly shaped and immovable non-magnetic sleeve. Rotation of the core moves developer of the Miskinis and Jadwin type along a first vertical and then horizontal path to and through the development zone. After the development zone, the non-magnetic shell drops off toward a developer sump where the developer falls for mixing. To assist in the transport of developer around the shell the upper portion of the shell is made somewhat rough. The roughened surface assists in the movement of developer as developer flips or tumbles in response to the changing magnetic field. The portion of the shell downstream of the development position that slopes most sharply toward the sump is made smooth to facilitate the fall of developer into the sump. See also, U.S. Pat. Nos. 4,884,109; 4,956,668 and 4,922,302. None of these structures show a gating or valving device for stopping the flow of developer since the device was designed for single-color apparatus.